Who is Halo 5's mystery Spartan?

Not Cortana Or Palmer, Apparently

Halo 5: Guardians' reveal artwork raised eyebrows across the internet by relegating the familiar armour of Spartan-117 (John to his mates) to the bottom of the banner, in place of an as-yet unnamed character wearing MJOLNIR tech.

We previously suspected a couple of series mainstays, but apparently we're way off piste.

First and foremost, we suspected that the mystery Spartan was none other than Sarah Palmer, who were were introduced to in Halo 4 and its Spartan Ops mini-campaign. The armour shares several similarities, especially in terms of the helmet shape and visor colour, while fleshing out her character would make sense considering that she's one of the major new cast members. Have a look at her MJOLNIR rig below.

Some fans also suspected that the enigmatic figure might even be Cortana in a new physical form - unlikely, but possible.

However, 343 Industries has squashed both of these guesses in a new tweet, hailing from executive producer Josh Holmes. Not only is he neither Cortana nor Palmer, but he's also a "he."

For everyone speculating about the mysterious Spartan in Halo 5: Guardians, he’s not Palmer (or Cortana!). He’s a NEW character. :) #Halo